Production of ethylbenzene

ABSTRACT

Benzene is efficiently recovered and the alkylating process is made to run more efficiently to produce ethylbenzene in the process of alkylating benzene with dilute ethylene by recirculating a large volume of polyethylbenzene to efficiently recover the benzene in the off-gases, splitting the benzene-rich polyethylbenzene scrubber effluent, returning a small approximate reaction equilibrium quantity of polyethylbenzene to the reactor, and then processing both the remaining benzene-rich scrubber effluent together with the total reactor effluent to recover benzene, ethylbenzene and residual polyethylbenzene.

United States Patent Helzner 1 Sept. 12, 1972 [541 PRODUCTION OFETHYLBENZENE Primary Examiner-Curtis R. Davis [72] Inventor. E. Helzner,Marblehead, Attorney sol B wiczer [73] Assignee: The Badger Company,Inc., Cam- [57] ABSTRACT bndgeMass Benzene is efficiently recovered andthe alkylating [22] Filed: Sept. 18, 1970 process is made to run moreefficiently to produce ethylbenzene in the process of alkylating benzenewith [21] dilute ethylene by recirculating a large volume ofpolyethylbenzene to efficiently recover the benzene in 52 U.S.Cl...260/67l R the Off-gases, Splitting the benqene-rich p y sd- 51 Int. Cl..c07 3/52 benzene Scrubber emuem rewmmg Small PP f ..260 671 R mateequilibrium quantity Pdyethyl- [58] Fleld 0 Search benzene to thereactor, and then processing both the remaining benzene-rich scrubbereffluent together [56] References cued with the total reactor effluentto recover benzene,

UNITED TA E PA ethylbenzene and residual polyethylbenzene.

3,255,269 6/1966 Gilman et al. ..260/671 5 Claim s, 1 Drawing FigureOFF-GAS '62 CATALYST SCRU BEER (39 /4 STFZSERLZ'GE 6+ BENZENE M /z 40 58SETTLER l ETHYLENE I EXTRACTOR 1 -35 was I r34 46 l STORAGE I 449 LBENZENE ETHYLBENZENE .E.B.

I RECOVERY RECOVERY RECOVERY PATENTEDSEP 12 I972 OFF -GAS REACTORscauaas CATALYST /4 FEB.

Q 15 STORAGE 64' asuzeue M I f /z 40 8 l SETTLER I ETHYLENE l0 42 IEXTRACTOR l 20 I I 36 /9 1 40 I 20 ,34 45 I STORAGE I 536 i 48- 4BENZENE ETHYLBENZENE 22.5. I RECOVERY RECOVERY aecovsav FEB. HEAVYmasmus mvm'ron ALBERT E. HELZNER J [A )i/d fH A'I'TORNICY PRODUCTION OFETHYLBENZENE This invention relates to the improved production ofethylbenzene. More particularly, this invention relates to improvedrecovery of benzene from off-gases produced in ethylbenzene synthesis byalkylation of benzene with dilute ethylene-containing gases.

According to the present invention the benzene is economically recovered'by large volume scrubbing of the off-gases with polyethylbenzene in asingle scrubber to recover substantially all of the benzene. Thebenzene-rich polyethylbenzene from the scrubber is split into a recyclestream to the reactor to return an equilibrium-maintaining quantity ofpolyethylbenzene from the scrubber, and a polyethylbenzene recoverystream, the latterbeing preferably jointly processed with the reactoreffluent to recover all of the liquid values.

In the production of ethylbenzene by catalytic reaction of benzene andethylene in the presence of an alkylation catalyst, such as promotedFriedel-Crafts or the like, significant economy in the reaction has beenfound to be present in the use of dilute ethylene feeds usuallycontaining less than 50 percent, and as low as 35 percent ethylenefandusually not more than 75 percent ethylene, the balance being largelyinert gases such as ethane, methane and hydrogen. Such reaction is oftencarried out at increasingly high pressures and temperatures, variablesomewhat with the catalyst in the range of about 125 to 300F, and apressure ranging from about atmospheric to about 100 psig.

This reaction mixture contains ethylbenzene reaction product andunreacted benzene as well as a smaller quantity of higherpolyethylbenzenes and portions of the catalyst, all ofthe componentsofthe reaction mixture being variable with the equilibrium conditionsestablished by the temperature, pressure and catalyst.

When a relatively pure ethylene feed has been used in the reaction, thequantity of off-gases isusually small and the normal recycle requirementof polyethylbenzene back to the reactor has provided ample scrubbingfluid to recover the small quantity of unreacted benzene in the off-gas.However, the reaction has been generally inefficient using diluteethylene feed in that the large volume of off-gases has carried anexcessive quantity of unreacted benzene whose recovery has beenattempted by scrubbing, usually in several scrubbers, with ethylbenzeneand/or polyethylbenzene as scrubbing fluid, with all of the benzene-richpolyethylbenzene from the scrubbers being recycled to the reactor.

The recirculation of polyethylbenzene via the scrubber for reclaiming ofthe benzene has been inefficient largely because the equilibriumcomposition does not contain enough polyethylbenzene for efficientbenzene recovery by a scrubbing of the off-gases therewith.

According to the present invention, a large volume scrubber feed isfirst made available in the storage tank, sufficient to allow largevolume scrubbing of the offgases in a single scrubber by independentcirculation of the polyethylbenzene from storage, for efficient removalof benzene therefrom. The rich polyethylbenzene scrubber solution ofrecovered benzene is separated by splitting into two streams. Thesmaller quantity of benzene-rich recycle polyethylbenzene in quantity ofabout to percent is returned to the reactor. This stream is preferablyadjusted in quantity to be only sufficient to maintain the normalequilibrium concentration of polyethylbenzene in the reactor variable,as stated, within such range with the particular reaction conditions andcatalyst as maintained in the reactor. The larger volume stream ofpolyethylbenzene scrubber solution is reprocessed with the totalreaction product effluent from the reactor to recover benzeneindependently as total recovered benzene, including that portion of thebenzene whichremained with the liquid reaction product and recovered bydistilling for ultimate return to the reactor feed.

By this means only a single scrubber is needed to remove substantiallyall of the benzene contained in the off-gases, and only the equilibriumquantity of polyethylbenzene needed to maintain the reactor equilibriumis recycled to the reactor. The remaining polyethylbenzene accumulatedin the storage is merely recirculated in large volume to the singlescrubber for its efficient operation to recover substantially all of theunreacted benzene using a'dilute ethylene alkylation feed. 4

Important economies are available in this procedure to recover all ofthe benzene in the off-gases in a single scrubber; to recirculate only abenzene-rich equilibrium quantity of polyethylbenzene to the reactor,increasing the reactor efficiency thereby; while providing a largeenough quantity of polyethylbenzene for scrubbing purposes for efficientoperation of the single scrubber. Since benzene remaining in the liquidreaction product is removed in a first distillation column for itsrecovery in any case, the compositing of total reactor effluent liquidpassing thereto with the excess circulation quantity of scrubber liquidrich in benzene, for total benzene recovery from the combined liquidsphase, only increases the quantity of benzene passing overhead and isnot an extra step.

The invention is further described by reference to the single sheet ofdrawing which shows diagrammatically the processing arrangement ofoperating units.

As shown therein, dilute ethylene-containing gases in line 10, benzenein line 12, and catalyst through line 14, are simultaneously passed tothe reactor 16. A recycle solution of benzene in polyethylbenzene fromscrubber 18 is passed by way of lines 19 and 20 to the reactor 16, therecycle solution being one of a split scrubber effluent passing inquantity substantially to maintain the polyethylbenzene content atequilibrium, variable with the exact process, temperature and catalystof reactor 16. Overhead off-gases comprising largely inert gasesincluding some unreacted ethylene and benzene, together with somereactor acid, pass overhead by way of line 22 and are cooled in a cooler24. The condensed liquids form cooler 24 are returned to reactor 16 byway of line 26, and the gases pass to the bottom of scrubber 18 by wayof line 28.

A large scrubbing volume of polyethylbenzene is taken from storage tank30 and passed by way of line 32 to the top of scrubber l8,countercurrent to the flow of off-gas therethrough to contact theoff-gas with at least 10 parts of polyethylbenzene to 1 part ofbenzenefree off-gas by weight. More usually up to 50 parts ofpolyethylbenzene scrubbing liquid is passed through line 32 per unitweight of benzene-free off-gas, to form a benzene-rich polyethylbenzenesolution which is withdrawn through line 19. The benzene-richpolyethylbenzene scrubber effluent is divided and, as stated above, anapproximate equilibrium quantity is passed as a split stream throughline and recycled to the reactor 16. A second stream consisting of arecirculated volume of benzene-rich polyethylbenzene split from thescrubber effluent is continued in the system by way of line 34. Thevolume of polyethylbenzene solution of benzene in line 34 corresponds tothe volume of polyethylbenzene withdrawn from storage tank from line 32less the equilibrium volume separated in line 20.

The reaction product liquid including catalyst, ethylbenzene,polyethylbenzene, unreacted benzene and other minor products present insaid reaction product are withdrawn as reactor effluent from the bottomof reactor 16, and passed by way of line 36, joining the splitrecirculation stream of benzene-rich polyethylbenzene in line 34, bothpassing to a settling tank 38 by way of line 39. The catalyst, such asaluminum chloride, is separated by settling tank 38 and is recycled atleast in part (not shown) to catalyst inlet feed line 14 to the reactor16. The clear reaction liquid passes by way of line 40 to an extractionunit 42 in which the catalyst acid or promoter is separated by washing.The washed reaction product passes by line 44 to storage 46. Thereaction liquid is then purified by distillation, passing by way of line48 to a column 50 from which total unreacted benzene is withdrawnoverhead through a line 52 and may be recycled to the reactor or passedto benzene storage (not shown). The heavier liquids of the reactionmixture are withdrawn at the bottom of column 50 through line 53 andpassed to an ethylbenzene recovery column 54, the ethylbenzene beingdistilled overhead and removed through line 56, passing to ethylbenzenestorage (not shown). The polyethylbenzenes are withdrawn from the bottomof column 54 through line 58 and sent to a polyethylbenzene column 60,the diethylbenzenes and possibly some triethylbenzenes passing overheadthrough line 62, passing thence to storage tank 30. A small quantity ofexcess polyethylbenzene may be withdrawn through line 64 from time totime after the storage tank 30 has been substantially filled.

In this manner all of the liquid benzenes as contained in therecirculated polyethylbenzene in line 34 as well as that withdrawn withthe reaction mixture from the bottom of the reactor 16 is removed asdistillate from the top of column 50. Only a single gas scrubber 18 isneeded for efficient removal of all of the volatile benzenes passingoverhead with the off-gases through lines 22 and 28 to the scrubber 18.The storage tank 30 is initially supplied from an outside source withenough polyethylbenzene for return through line 32 to the top ofscrubber 18 for washing the off-gas in large volume ratio, sufficient toefficiently remove substantially all of the benzene from the off-gases.This large excess of polyethylbenzene is then recirculated to the systemfor recovery of the benzene in column 50 by way of line 34 after firstseparating an equilibrium quantity of polyethylbenzene for return to thereactor through line 20. Heavier polyethylbenzenes are withdrawn fromthe bottom of column 60 by way of line 66 and are thence Withdrawn fromthe system.

The following example further illustrates the practice of thisinvention:

EXAMPLE I In a typical installation, aluminum chloride promoted byhydrochloric acid as catalyst is passed to a reactor operated at atemperature of about 150F, typically at a pressure of about 50 psig. Adilute ethylene feed comprising about 40 percent ethylene and thebalance being substantially ethane with small quantities of methane andhydrogen together with an excess of benzene are simultaneously passed tothe reactor. The overhead gases from the reactor are cooled to about Fand those gases still containing about 10 percent of benzene are passedto the bottom of the scrubber. Cold polyethylbenzene at a temperature ofabout l20F is withdrawn from storage and is pumped to the top of thescrubber and is then sprayed countercurrently to the gas passingupwardly therethrough in sufficient volume to extract the benzene. About10 pounds of polyethylbenzene per pound of benzene-free off-gas isemployed, producing about a 0.5 percent benzene solution therein. Thebenzene solution is polyethylbenzene is divided in ratio of about 3 tol, varied as required to meet the desired equilibrium composition I ofthe reactor; the one volume flow passing through line 20 with a threevolume flow through line 34.

The following material balance is typical:

Line Stream Composition Flow Rate, LB/HR At the start of the operation,the storage tank 30 is inventoried with polyethylbenzenefrom an externalsource to provide a supply of'polyethylbenzene for other start-upoperations. Scrubber feed is withdrawn from storage via line 32 and therecirculation stream from the scrubber is sent to the settler tank 38via lines 19, 34 and '39. The polyethylbenzene is then processed throughthe extraction and distillation sections and returned to storage tank30. The flow of recycle feed in line 20 in varied as desired to satisfyreactor start-up conditions. When normal operations obtain, the recyclefeed in line 20 is increased to approximately that required for reactorequilibrium conditions so that the split of recycle feed to the reactorand the recirculation stream are so divided that about one-third of thescrubber effluent is recycled to the reactor and twothirds to recovery.

It will be seen, consequently, that the single scrubber is efficientlyoperated with a large volume of polyethylbenzene scrubbing liquid, madepossible by an initial inventory of a large enough quantity in storageto supply sufficient quantity to allow the large volume of liquid forscrubbing of the total-off-gas. During normal reactor operationequilibrium conditions are controlled so that no polyethylbenzene isconsumed or produced. That large volume of effluent from the scrubber issplit to return only enough benzene-enriched polyethylbenzene to thereactor to maintain this equilibrium. While the polyethylbenzene can beredistilled to separate much heavier from intermediatepolyethylbenzenes, the bottoms of the ethylbenzene still can be usedwithout further purification as scrubber liquid.

Such other variations as known in the art of synthesis of ethylbenzenesmay be applied here.

What is claimed is:

1. In a process for forming ethylbenzene by alky-lating benzene in acatalytic reactor and recovering the reaction products including benzenefrom the offgases, the steps of a. catalytically reacting a diluteethylene gas with benzene in a reactor in the presence of a catalyst andabout 5 to 35 percent of recycle polyethylbenzene based upon a totaloff-gas scrubber effluent;

b. withdrawing liquid reaction product from the reactor and processingthe same in a series of liquid recovery steps to recover benzene,monoethylbenzene and polyethylbenzene separately by distillation;

c. passing the off-gas of said reaction containing benzene vapors fromthe reactor to a scrubber;

d. passing a large wash volume of polyethyl-benzene to said scrubber toremove the benzene from said off-gases;

e. splitting the recovered liquid benzene-rich scrubber effluent fromsaid scrubbing step into two separate streams;

f. passing one of said scrubber effluent streams in quantity of about 5to 35 percent of said scrubber effluent as recycle to said reactor;

g. passing the second scrubber effluent stream together with said liquidreaction product withdrawn from said reactor to said liquid recovery;

and

h. recirculating recovered polyethylbenzene to said scrubber.

2. The process as defined in claim 1 wherein the benzene-richpolyethylbenzene scrubber liquid effluent is divided into split streams,and the stream which is recycled to said reactor is in quantityapproximating the equilibrium quantity of polyethylbenzene formed in thealkylation reaction.

3. The process as defined in claim 1 wherein at the start of saidreaction polyethylbenzene is inventoried in storage in substantialquantity to supply a large work volume for scrubbing said off-gases, andafter said inventory, the polyethylbenzene is then passed from storageto said off-gas scrubber in large volume, independently of thepolyethylbenzene requirement of the reaction.

4. The process as defined in claim 1 wherein the benzene recovered isreused as a portion of the benzene feed to said reactor.

5. The process as defined in claim 1 wherein the dilute ethylene feed tosaid reactor is a refinery ethylene gas containing less than about 50percent of ethylene, the remainder being inert refinery gases.

2. The process as defined in claim 1 wherein the benzene-richpolyethylbenzene scrubber liquid effluent is divided into split streams,and the stream which is recycled to said reactor is in quantityapproximating the equilibrium quantity of polyethylbenzene formed in thealkylation reaction.
 3. The process as defined in claim 1 wherein at thestart of said reaction polyethylbenzene is inventoried in storage insubstantial quantity to supply a large work volume for scrubbing saidoff-gases, and after said inventory, the polyethylbenzene is then passedfrom storage to said off-gas scrubber in large volume, independently ofthe polyethylbenzene requirement of the reaction.
 4. The process asdefined in claim 1 wherein the benzene recovered is reused as a portionof the benzene feed to said reactor.
 5. The process as defined in claim1 wherein the dilute ethylene feed to said reactor is a refineryethylene gas containing less than about 50 percent of ethylene, theremainder being inert refinery gases.